FW1 - NAT hide problem

["Andy Davis" <andy () fiveacre demon co uk>]

Hi I hope someone can help me with this problem:

I've just installed FW1 on an NT box, it has two interfaces - an ISDN RAS connection to the Internet and a ethernet 
connect to an internal network containing a Linux box. I've been trying to set it up so that the internal addresses 
192.168.10.x are hidden by the external address (valid address) of the firewall.

Please could someone explain in simple terms how to configure this setup. Currently when I ping from the linux box to 
the Internet the echo-request packet reaches the firewall as I can see it appear on the log but the echo-reply never 
appears. Also whenever I boot my NT box the MAC address of the RAS interface changes (I presume because it's not a real 
physical interface - it this the problem?

Thanks in advance,

Andy Davis.